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During Prophase I tetrad formation takes place. Tetrad contains four sister chromatids.

Option b is correct because the Tetrad arrangement of chromosomes is mediated by a protein lattice called the synaptonemal complex. It is formed during early prophase I of meiosis I. It helps to bind the chromatin of the homologous chromosomes.

Option a is incorrect because chromosomes are attached to the synaptonemal complex and by cohesion protein at the centromere. The Synaptonemal complex is most important in the arrangement of tetrads.

Option c is incorrect because tetrads are bound together at the chiasmata. The Synaptonemal complex is most essential in forming the tetrads.

Option d is incorrect because the synaptonemal complex is most important in the arrangement of tetrads.